Plants Toxic to Horses

  • 01 of 11

    Deadly Nightshade

    deadly nightshade
    Dorit Bar-Zakay / Getty Images

    These common weeds, trees, plants, and shrubs are toxic to horses and ponies. Learn to identify these plants in your pastures and yards.

    Deadly nightshade likes sandy soil and thrives even in dry conditions. It has a white star-shaped flower and the fruit looks like a large black currant. All parts of this plant are toxic to humans and pets.

    The leaves are dark green and smooth-textured, somewhat similar to that of a tomato plant. It is in the same family as the tomato, potato, and pepper plants which is why you don't want your neighbor pitching his garden scraps over your fence—nightshades can be difficult to eradicate.

    Horses are unlikely to eat nightshade or any other toxic plant unless there is no other feed available or it is baled into the hay and eaten accidentally. Signs of nightshade poisoning may include:

    • colic-like symptoms
    • loss of muscle control
    • disorientation
    • dilated pupils
    • death
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  • 02 of 11


    buttercup flowers
    Paul Mansfield Photography / Getty Images

    The flowers are yellow and cup-shaped with sharply lobed leaves off of a thin stem. The grass around them will be well grazed. Horses will avoid eating buttercups if there is more desirable feed available. After a hard frost or dried in hay, buttercups are no longer toxic.

    Buttercups may cause:

    • irritation of the mouth area
    • colic-like symptoms
    • diarrhea
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  • 03 of 11

    Bracken Fern

    fern plant

    Bracken fern is very common, growing along roadsides, in fields, in light bush areas, and even gardens. In the spring 'fiddleheads' unfurl into triangular fronds up to 3ft (1m) high. Bracken fern dried and baled into hay is still toxic. If a horse eats a large quantity of this fern the toxins can cause a vitamin B1 deficiency.

    Symptoms of bracken fern poisoning may include:

    • loss of coordination
    • depressed heart rate
    • arrhythmia
    • weight loss
    • eventual death if not promptly treated


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  • 04 of 11

    Horse Tails

    horetail plant
    PhotoAlto/Frederic Cirou/Getty Images

    The soil around my old property is largely sand and gravel. It drains quickly, making it perfect for this variety of horsetail. Other varieties grow in more marshy areas. If the plant is dried and baled into hay the toxin may have a greater effect than in the fresh plant. The toxin in this plant destroys vitamin B in the horse's blood.

    Symptoms of Horsetail poisoning are:

    • weakness
    • stumbling
    • arrhythmia of increased pulse
    • irritability
    • death


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  • 05 of 11

    Lamb's Quarters (or Pigweed)

    lambs quarter plant
    Carrol & Carrol / Getty Images

    In some areas, this plant is called pigweed or lamb's quarters. It has smooth, light-colored leaves and a woody red stem. The 'flower' looks rather like a small pale green cauliflower cluster.

    A horse would have to eat a large number of lamb's quarters for the toxin to take effect. Unless there is no other feed available it is unlikely a horse will eat this plant.

    If a horse consumes a large number of lamb's quarters symptoms may include:

    • weakness
    • lack coordination
    • respiratory distress
    • coma
    • kidney failure
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  • 06 of 11

    Lily of the Valley

    lily of the valley
    Westend61/Getty Images

    It's a lovely spring-blooming perennial bulb, but it's deadly to horses. Does this grow in your flower garden?

    This common garden plant is toxic to humans and pets, including horses. Lily of the Valley is unlikely to be growing in a pasture. It could be accidentally ingested if someone were to throw garden clippings close to a fence line where curious horses might be able to reach. Garden and lawn clippings should be disposed of out of reach of horses.

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  • 07 of 11


    Deb Perry/Getty Images

    Milkweed is a very common pasture plant. Elliptical shaped leave branch off of a central stem. Inside the plant is a white, sticky sap. The flowers grow in a ball-shaped cluster and when in full bloom are a lavender color. The pods develop to about 3" and in fall split open to release brown seeds that float through the air on downy fibers. All parts of the plant are toxic. Living and dried plants (accidentally baled into hay) are toxic. Like most toxic plants horses will avoid milkweed unless they have no other food source. Signs of milkweed poisoning are:

    • disorientation
    • loss of muscular control
    • spasming
    • rapid and weak pulse
    • respiratory paralysis

    Milkweed poisoning is rarely fatal.

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  • 08 of 11


    amaranthus pigweed
    Bill Barksdale / Getty Images

    Pigweed can be very toxic if eaten in large quantities. Horses are unlikely to eat this plant unless there is no other food available. This weed seems to grow everywhere, from pastures to vegetable gardens, roadsides to barnyards. It is still toxic if dried and baled into hay. Pigweed and its relative lamb's quarters can cause kidney failure. Other symptoms of pigweed ingestion may include:

    • respiratory distress
    • weakness
    • lack of coordination
    • coma


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  • 09 of 11

    Red Maple

    red maple leaves
    Xia Yuan / Getty Images

    The bark of red maples is smooth and grayish. The twigs are reddish-brown.

    The fresh leaves are considered relatively safe, but wilted and fallen leaves can be toxic—but tasty, to horses. The toxins affect the red blood cells. Three pounds of ingested red maple leaves are considered lethal.

    Leaves can remain toxic for several weeks after they've fallen. Don't dispose of red maple leaves in manure piles or compost heaps that might be in reach of your horses. Red maple leaves can cause problems if baled into hay.

    Red maples grow throughout the eastern United States and Canada.

    Symptoms of red maple poisoning are:

    • depression
    • dark brown urine
    • rapid pulse
    • increased respiration
    • coma
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  • 10 of 11

    Red Oak

    oak tree
    John Lawson / Getty Images

    Various varieties of oaks live throughout North America. Horses will eat the leaves if there is no other food available. Water may be contaminated by fallen leaves. Acorns are also toxic if eaten in quantity.

    Signs of oak poisoning are:

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  • 11 of 11

    St. John's Wort

    st. johns wort
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    From mid-July to mid-August St. John's Wort blooms in dry sandy soil. If you crush the flowers between your fingers, it will leave a rusty reddish stain. Some people soak the flowers in a vegetable oil base to make what is believed to be a healing oil. St. John's Wort causes photosensitivity, whether it is ingested or as oil applied to the skin.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.